Do I need memcached with Opcache ?
I don't know anything about caching other than having read that people use APC/Opcache/Memcache/Memchached/Varnish ... to makes PHP go faster :)
So, I tried APC last week since I was on PHP5.4, but then updated my to PHP5.5 so I could use Opcache. So, now that Opcache is working, I need to even make my wordpress site faster, and since I have heard that APC is not compatible with opcache, I would like to know if memcached is OK to use, as I am almost certain varnish is OK because it is not related to PHP.
So, will using memcached further improve my site?
OPcache is for accelerating code access. memcached is for accelerating data access. They are completely different, and completely independent.
While OpCache doesn't support the user-side caching functionality of APC, it can still be a useful tool, and so the Pecl module, APCU was extracted from the original. It's entirely compatible with the original, but leaves the zend-code cache for OpCache.